Choudhury, Abu Turab Mohmmad Ali, and Mohammad Khanif Yousop. 2009. “A 15N Tracer Study to Evaluate the Effects of Nitrogen and Copper Fertilization on Fertilizer Nitrogen Efficiency in Rice Production: 15N Tracer Study for N and Cu Fertilization in Rice”. Biological Sciences - PJSIR 52 (1):53-58. https://v2.pjsir.org/index.php/biological-sciences/article/view/510.